Tasimelteon (Hetlioz™) is a selective agonist at melatonin MT1 and MT2 receptors which are found in high density in the hypothalamic suprachiasmatic nuclei. In January 2014, Tasimelteon was approved by the United States Food and Drug Administration (FDA) for the treatment of Non-24-Hour Sleep-Wake Disorder. Its chemical name is [(1R-2R)—N-[2-(2,3-dihydrobenzofuran-4-yl)cyclopropylmethyl]propanamide], and the molecular formula is C12H19NO2. The structure is as follows:

Non-24, also referred to as Non-24-Hour Sleep-Wake Disorder or Non-24-Hour sleep cycle Disorder, occurs when individuals, primarily blind with no light perception, are unable to synchronize their endogenous circadian pacemaker to the 24-hour light/dark cycle. Individuals with Non-24 have abnormal night sleep patterns, accompanied by difficulty staying awake during the day.
It is estimated that approximately 100,000 people in the United States suffer from Non-24 and cannot feel enough light to set up a normal night sleep schedule, although most people who are completely blind can still feel the light well and can prevent Non-24. Non-24 occurs at any age. Clinical trials in two totally blind subjects diagnosed with non-24 demonstrated the efficacy of Tasimelteon in reducing both nighttime wakefulness and daytime napping. Physiologic monitoring revealed that Tasimelteon resulted in a higher proportion of individuals becoming entrained to the 24-hour cycle compared with placebo.
Patents WO2011009102, CN102675268, CN103087019 and CN104327022 disclose the production methods for Tasimelteon, but don't disclose the crystalline polymorphism of the compound. The patents describe no crystallographic aspect of the compound. In general, active pharmaceutical ingredients (APIs) are capable of existing in polymorphic forms.
Different polymorphs can display marked differences in their key physicochemical and biopharmaceutical performance, including stability, melting point, solubility, dissolution, and so on. These properties can directly affect the production, the storage and the use of APIs and their preparations. Thus, searching for various crystal modifications are essential parts of drug development.